Application Security report: 2024 update

Over the last twelve months, the Internet security landscape has changed dramatically. Geopolitical uncertainty, coupled with an active 2024 voting season in many countries across the world, has led to a substantial increase in malicious traffic activity across the Internet. In this report, we take a look at Cloudflare’s perspective on Internet application security.

This report is the fourth edition of our Application Security Report and is an official update to our Q2 2023 report. New in this report is a section focused on client-side security within the context of web applications.

Throughout the report we discuss various insights. From a global standpoint, mitigated traffic across the whole network now averages 7%, and WAF and Bot mitigations are the source of over half of that. While DDoS attacks remain the number one attack vector used against web applications, targeted CVE attacks are also worth keeping an eye on, as we have seen exploits as fast as 22 minutes after a proof of concept was released.

Focusing on bots, about a third of all traffic we observe is automated, and of that, the vast majority (93%) is not generated by bots in Cloudflare’s verified list and is potentially malicious.

API traffic is also still growing, now accounting for 60% of all traffic, and maybe more concerning, is that organizations have up to a quarter of their API endpoints not accounted for.

We also touch on client side security and the proliferation of third-party integrations in web applications. On average, enterprise sites integrate 47 third-party endpoints according to Page Shield data.

It is also worth mentioning that since the last report, our network, from which we gather the data and insights, is bigger and faster: we are now processing an average of 57 million HTTP requests/second (+23.9% YoY) and 77 million at peak (+22.2% YoY). From a DNS perspective, we are handling 35 million DNS queries per second (+40% YoY). This is the sum of authoritative and resolver requests served by our infrastructure.

Maybe even more noteworthy, is that, focusing on HTTP requests only, in Q1 2024 Cloudflare blocked an average of 209 billion cyber threats each day (+86.6% YoY). That is a substantial increase in relative terms compared to the same time last year.

As usual, before we dive in, we need to define our terms.

Throughout this report, we will refer to the following terms:

• Mitigated traffic: any eyeball HTTP* request that had a “terminating” action applied to it by the Cloudflare platform. These include the following actions: BLOCK, CHALLENGE, JS_CHALLENGE and MANAGED_CHALLENGE. This does not include requests that had the following actions applied: LOG, SKIP, ALLOW. They also accounted for a relatively small percentage of requests. Additionally, we improved our calculation regarding the CHALLENGE type actions to ensure that only unsolved challenges are counted as mitigated. A detailed description of actions can be found in our developer documentation. This has not changed from last year’s report.

• Bot traffic/automated traffic: any HTTP* request identified by Cloudflare’s Bot Management system as being generated by a bot. This includes requests with a bot score between 1 and 29 inclusive. This has not changed from last year’s report.

• API traffic: any HTTP* request with a response content type of XML or JSON. Where the response content type is not available, such as for mitigated requests, the equivalent Accept content type (specified by the user agent) is used instead. In this latter case, API traffic won’t be fully accounted for, but it still provides a good representation for the purposes of gaining insights. This has not changed from last year’s report.

Unless otherwise stated, the time frame evaluated in this post is the period from April 1, 2023, through March 31, 2024, inclusive.

Finally, please note that the data is calculated based only on traffic observed across the Cloudflare network and does not necessarily represent overall HTTP traffic patterns across the Internet.

^{*When referring to HTTP traffic we mean both HTTP and HTTPS.}

Compared to the prior 12-month period, Cloudflare mitigated a higher percentage of application layer traffic and layer 7 (L7) DDoS attacks between Q2 2023 and Q1 2024, growing from 6% to 6.8%.

Figure 1: Percent of mitigated HTTP traffic increasing over the last 12 months

During large global attack events, we can observe spikes of mitigated traffic approaching 12% of all HTTP traffic. These are much larger spikes than we have ever observed across our entire network.

As the Cloudflare platform continues to expose additional signals to identify potentially malicious traffic, customers have been actively using these signals in WAF Custom Rules to improve their security posture. Example signals include our WAF Attack Score, which identifies malicious payloads, and our Bot Score, which identifies automated traffic.

After WAF and Bot mitigations, HTTP DDoS rules are the second-largest contributor to mitigated traffic. IP reputation, that uses our IP threat score to block traffic, and access rules, which are simply IP and country blocks, follow in third and fourth place.

Figure 2: Mitigated traffic by Cloudflare product group

Zero-day exploits (also called zero-day threats) are increasing, as is the speed of weaponization of disclosed CVEs. In 2023, 97 zero-days were exploited in the wild, and that’s along with a 15% increase of disclosed CVEs between 2022 and 2023.

Looking at CVE exploitation attempts against customers, Cloudflare mostly observed scanning activity, followed by command injections, and some exploitation attempts of vulnerabilities that had PoCs available online, including Apache CVE-2023-50164 and CVE-2022-33891, Coldfusion CVE-2023-29298 CVE-2023-38203 and CVE-2023-26360, and MobileIron CVE-2023-35082.

This trend in CVE exploitation attempt activity indicates that attackers are going for the easiest targets first, and likely having success in some instances given the continued activity around old vulnerabilities.

As just one example, Cloudflare observed exploitation attempts of CVE-2024-27198 (JetBrains TeamCity authentication bypass) at 19:45 UTC on March 4, just 22 minutes after proof-of-concept code was published.

Figure 3: JetBrains TeamCity authentication bypass timeline

The speed of exploitation of disclosed CVEs is often quicker than the speed at which humans can create WAF rules or create and deploy patches to mitigate attacks. This also applies to our own internal security analyst team that maintains the WAF Managed Ruleset, which has led us to combine the human written signatures with an ML-based approach to achieve the best balance between low false positives and speed of response.

CVE exploitation campaigns from specific threat actors are clearly visible when we focus on a subset of CVE categories. For example, if we filter on CVEs that result in remote code execution (RCE), we see clear attempts to exploit Apache and Adobe installations towards the end of 2023 and start of 2024 along with a notable campaign targeting Citrix in May of this year.

Figure 4: Worldwide daily number of requests for Code Execution CVEs

Similar views become clearly visible when focusing on other CVEs or specific attack categories.

DDoS attacks remain the most common attack type against web applications, with DDoS comprising 37.1% of all mitigated application traffic over the time period considered.

Figure 5: Volume of HTTP DDoS attacks over time

We saw a large increase in volumetric attacks in February and March 2024. This was partly the result of improved detections deployed by our teams, in addition to increased attack activity. In the first quarter of 2024 alone, Cloudflare’s automated defenses mitigated 4.5 million unique DDoS attacks, an amount equivalent to 32% of all the DDoS attacks Cloudflare mitigated in 2023. Specifically, application layer HTTP DDoS attacks increased by 93% YoY and 51% quarter-over-quarter (QoQ).

Cloudflare correlates DDoS attack traffic and defines unique attacks by looking at event start and end times along with target destination.

Motives for launching DDoS attacks range from targeting specific organizations for financial gains (ransom), to testing the capacity of botnets, to targeting institutions and countries for political reasons. As an example, Cloudflare observed a 466% increase in DDoS attacks on Sweden after its acceptance to the NATO alliance on March 7, 2024. This mirrored the DDoS pattern observed during Finland’s NATO acceptance in 2023. The size of DDoS attacks themselves are also increasing.

In August 2023, Cloudflare mitigated a hyper-volumetric HTTP/2 Rapid Reset DDoS attack that peaked at 201 million requests per second (rps) – three times larger than any previously observed attack. In the attack, threat actors exploited a zero-day vulnerability in the HTTP/2 protocol that had the potential to incapacitate nearly any server or application supporting HTTP/2. This underscores how menacing DDoS vulnerabilities are for unprotected organizations.

Gaming and gambling became the most targeted sector by DDoS attacks, followed by Internet technology companies and cryptomining.

Figure 6: Largest HTTP DDoS attacks as seen by Cloudflare, by year

Cloudflare has continued to invest heavily in our bot detection systems. In early July, we declared AIndependence to help preserve a safe Internet for content creators, offering a brand new “easy button” to block all AI bots. It’s available for all customers, including those on our free tier.

Major progress has also been made in other complementary systems such as our Turnstile offering, a user-friendly, privacy-preserving alternative to CAPTCHA.

All these systems and technologies help us better identify and differentiate human traffic from automated bot traffic.

31.2% of all application traffic processed by Cloudflare is bot traffic. This percentage has stayed relatively consistent (hovering at about 30%) over the past three years.

The term bot traffic may carry a negative connotation, but in reality bot traffic is not necessarily good or bad; it all depends on the purpose of the bots. Some are “good” and perform a needed service, such as customer service chatbots and authorized search engine crawlers. But some bots misuse an online product or service and need to be blocked.

Different application owners may have different criteria for what they deem a “bad” bot. For example, some organizations may want to block a content scraping bot that is being deployed by a competitor to undercut on prices, whereas an organization that does not sell products or services may not be as concerned with content scraping. Known, good bots are classified by Cloudflare as “verified bots.”

Unverified bots are often created for disruptive and harmful purposes, such as hoarding inventory, launching DDoS attacks, or attempting to take over an account via brute force or credential stuffing. Verified bots are those that are known to be safe, such as search engine crawlers, and Cloudflare aims to verify all major legitimate bot operators. A list of all verified bots can be found in our documentation.

Attackers leveraging bots focus most on industries that could bring them large financial gains. For example, consumer goods websites are often the target of inventory hoarding, price scraping run by competition or automated applications aimed at exploiting some sort of arbitrage (for example, sneaker bots). This type of abuse can have a significant financial impact on the target organization.

Figure 8: Industries with the highest median daily share of bot traffic

Consumers and end users expect dynamic web and mobile experiences powered by APIs. For businesses, APIs fuel competitive advantages, greater business intelligence, faster cloud deployments, integration of new AI capabilities, and more.

However, APIs introduce new risks by providing outside parties additional attack surfaces with which to access applications and databases which also need to be secured. As a consequence, numerous attacks we observe are now targeting API endpoints first rather than the traditional web interfaces.

The additional security concerns are of course not slowing down adoption of API first applications.

This is a two percentage point increase compared to last year’s report. Of this 60%, about 4% on average is mitigated by our security systems.

Figure 9: Share of mitigated API traffic

A substantial spike is visible around January 11-17 that accounts for almost a 10% increase in traffic share alone for that period. This was due to a specific customer zone receiving attack traffic that was mitigated by a WAF Custom Rule.

Digging into mitigation sources for API traffic, we see the WAF being the largest contributor, as standard malicious payloads are commonly applicable to both API endpoints and standard web applications.

Figure 10: API mitigated traffic broken down by product group

You cannot protect what you cannot see. And, many organizations lack accurate API inventories, even when they believe they can correctly identify API traffic.

Using our proprietary machine learning model that scans not just known API calls, but all HTTP requests (identifying API traffic that may be going unaccounted for), we found that organizations had 33% more public-facing API endpoints than they knew about. This number was the median, and it was calculated by comparing the number of API endpoints detected through machine learning based discovery vs. customer-provided session identifiers.

This suggests that nearly a quarter of APIs are “shadow APIs” and may not be properly inventoried and secured.

Most organizations’ web apps rely on separate programs or pieces of code from third-party providers (usually coded in JavaScript). The use of third-party scripts accelerates modern web app development and allows organizations to ship features to market faster, without having to build all new app features in-house.

Using Cloudflare's client side security product, Page Shield, we can get a view on the popularity of third party libraries used on the Internet and the risk they pose to organizations. This has become very relevant recently due to the Polyfill.io incident that affected more than one hundred thousand sites.

Cloudflare’s typical enterprise customer uses an average of 47 third-party scripts, and a median of 20 third-party scripts. The average is much higher than the median due to SaaS providers, who often have thousands of subdomains which may all use third-party scripts. Here are some of the top third-party script providers Cloudflare customers commonly use:

• Google (Tag Manager, Analytics, Ads, Translate, reCAPTCHA, YouTube)

• Meta (Facebook Pixel, Instagram)

• Cloudflare (Web Analytics)

• jsDelivr

• New Relic

• Appcues

• Microsoft (Clarity, Bing, LinkedIn)

• jQuery

• WordPress (Web Analytics, hosted plugins)

• Pinterest

• UNPKG

• TikTok

• Hotjar

While useful, third-party software dependencies are often loaded directly by the end-user’s browser (i.e. they are loaded client-side) placing organizations and their customers at risk given that organizations have no direct control over third-party security measures. For example, in the retail sector, 18% of all data breaches originate from Magecart style attacks, according to Verizon’s 2024 Data Breach Investigations Report.

Loading a third-party script into your website poses risks, even more so when that script “calls home” to submit data to perform the intended function. A typical example here is Google Analytics: whenever a user performs an action, the Google Analytics script will submit data back to the Google servers. We identify these as connections.

On average, each enterprise website connects to 50 separate third-party destinations, with a median of 15. Each of these connections also poses a potential client-side security risk as attackers will often use them to exfiltrate additional data going unnoticed.

Here are some of the top third-party connections Cloudflare customers commonly use:

• Google (Analytics, Ads)

• Microsoft (Clarity, Bing, LinkedIn)

• Meta (Facebook Pixel)

• Hotjar

• Kaspersky

• Sentry

• Criteo

• tawk.to

• OneTrust

• New Relic

• PayPal

This application security report is also available in PDF format with additional recommendations on how to address many of the concerns raised, along with additional insights.

We also publish many of our reports with dynamic charts on Cloudflare Radar, making it an excellent resource to keep up to date with the state of the Internet.